1. Field of the Invention:
This invention pertains to digital transmission of information.
2. Description of the Prior Art:
Non-Return-to-Zero (NRZ) data signals have the advantage of narrower bandwidths than some other types of transmission signals. A disadvantage of NRZ for data transmission is the absence of a frequency component at the bit rate. NRZ signals usually require a clock signal to accompany the data signals in order to interpret data correctly.
Other techniques for bit timing in NRZ add discrete frequency components at the bit rate or vary the duration of the information bits. Adding a sinusoid to the transmitted signal reduces the signal to noise ratio. If the timing sinusoid is added outside the band or the pulse duration of the information bits is varied, then a wider bandwidth is required than with the NRZ signals alone.
The invention herein described and claimed discloses a circuit and method for inserting a frequency component at the bit rate which does not increase the bandwidth requirement of NRZ and which causes no signal-to-noise degradation, but which can be linearly extracted at the receiver.